There are already several types of image compression techniques. There is one technique using orthogonal transformation that transforms time domain data to frequency domain data. The image compression technique with that orthogonal transformation realizes a relatively high compressibility ratio.
Numerous calculations are required for the above-mentioned orthogonal transformation. Accordingly, the scale of hardware needed to realize an image compression apparatus performing image compression by means of the orthogonal transformation becomes large. The techniques of image compression are expected to be applied to broader fields in the future. Also, in this respect, it is considered to be important that the image compressing apparatus be realized with hardware on a smaller scale while maintaining the high compressibility ratio. The same applies to an image decompressing apparatus that decompresses the compressed image.
Recently, in cars for example, there has been an increasing need to use video in multiple channels, as in the cases of installing several monitoring cameras and monitoring their video from the driver's seat, or utilizing the DVD or video of a car navigation system from the rear seat. In order to avoid complicated wiring due to the increased number of channels, the idea of installing a LAN in the car has been introduced so as to perform data transmission of the multiple channels by means of this LAN (vehicle-mounted LAN).
The requirements for the vehicle-mounted LAN are (1) being light weight (low cost), (2) having high image quality in both natural images and CG (Computer Graphics), and (3) having low delay. (3) Having low delay is required for transmitting the image of a vehicle-mounted camera for the security use. As the amount of data is large in a video (image), data compression must be performed with a reasonably high compressibility ratio in order to realize the low delay. Therefore, it is considered that image compression technology will be an essential technology for vehicle-mounted LANs in the future.
[Patent Document 1]
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